1. Field of the Invention
This invention relates to a ticket issuing device which issues a plurality of tickets as a single unit, and more particularly to a ticket issuing device having a thermal head for printing tickets to be issued.
2. Description of the Related Art
At airports, boarding tickets (or boarding passes), for passenger planes are issued by ticket issuing devices. In a case where a plurality of airlines share the same ticket issuing device, the device is connected to the host computer of the airline having the next departure flight, so as to print on paper the name of the airline, the boarding date, the place of departure and destinations, the flight number, passenger seat number, and other boarding information (or ticket information) sequentially supplied from the computer as printing data, and issue the printed paper in the form of boarding tickets.
Conventionally, a ticket issuing device having a thermal head formed with a plurality of heat generating elements is known. The ticket issuing device prints the boarding information on paper formed of ordinary paper material in combination with a heat transfer ribbon coated with fusible ink. When the heat generating elements of the thermal head are selectively driven to perform a printing operation, the fusible ink is partly melted by heat generated from the driven heat generating elements and transferred from the heat transfer ribbon to the paper. Fusible ink is superior to liquid ink as regards its quick-drying property, and therefore there is no possibility of the passengers hands or clothes being stained by the boarding tickets issued.
In order to issue the total number of boarding tickets required in a short period of time, the issuing speed of the ticket issuing device is raised to maximum by increasing the energization power supplied to the heat generating elements and reducing the energization time. However, the temperature of the thermal head is raised by the heat generated from the heat generating elements as a result of the printing operation being effected repeatedly, and such temperature increase may degrade the printing quality. Therefore, the issuing speed is limited so as not give rise to an increase in temperature such as would degrade the printing quality, when the printing operation is being effected repeatedly so as to issue a quantity of boarding tickets corresponding to the number of seats of, for example, a large-capacity airliner.
The issuing speed of the ticket issuing device is set appropriately so as to print all the boarding information in the form of ordinary characters on ticket paper. With such a ticket issuing device, a problem occurs when a large part of the boarding information is printed in the form of picture on ticket paper so as to issue unique boarding tickets. That is, if most of the heat generating elements are more frequently driven as a result of an increase in the printing density, the thermal head will be heated to a temperature higher than in the case of the normal printing operation in which all the boarding information is printed in the form of ordinary characters. If the temperature of the thermal head rises significantly, the ticket paper will be stained by fusible ink melted by the heat coming from that portion of the thermal head around the heat generating elements, with the result that the characters will be printed having thicker lines and their contours will become unclear. Moreover, the heat generating elements themselves may be damaged.
In order to solve the above problem, consideration has been given to the issuing speed being determined in the design process of the ticket issuing device appropriately, so as to print all the boarding information in the form of picture. However, the issuing speed will be lower than that in the conventional case.